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other world results, starting with the G0 forward
angle measurements to enable the determination
of individual strange and axial form factors.
Forward measurements results
For eighteen values of Q 2 , the asymmetries have
been measured simultaneously, the results of
Figure 2 Asymmetries and form factors
which are presented in Fig.2, together with the linear
combinations of G s E, G s M , extracted from the
asymmetries [3].
Figure 3 G s E, G s M and G e A determined by the G0
experiment forward and backward angle measurements
[4]. Results are compared to other experiments
[5], [6] and [9] and to recent calculations [7],
[8], [10] and [11].
Backward measurements results
Only two Q 2 regions have been explored at backward
angle because of time limitation. Combined
with the forward angle measurements it was possible
to extract all the form factors separately with
data from G0 only. The results are presented in
Fig.3 with some theoretical calculations.
Summary
In summary, we have measured forward angle parity
violating asymmetries in elastic electron-proton
in the range of Q 2 = 0.15 to 1.0 GeV 2 and backward
angle parityviolating asymmetries in elastic
electron-proton and quasielastic electron-deuteron
scattering at Q 2 = 0.221 and 0.628 GeV 2 . These
asymmetries determine the neutral weak interaction
analogs of the ordinary charge and magnetic
form factors of the nucleon, together with the effective
axial form factor. From the asymmetries we
have determined G s E, G s M, and G e A T=1 , which indicate
that the strange quark contributions to the
nucleon form factors are ~ 10%, and provide the
first information on the Q 2 dependence of G e A T=1 .
Future forward angle experiments at Q 2 = 0.63
GeV 2 at Jefferson Lab and Mainz will further improve
the precision of these determinations.Other new
data on parity violation will soon complement these
studies leading to a better knowledge of hadronic
effects at low Q 2 . The next challenge for the parityviolating
electron scattering is the search of physics
beyond the Standard Model, part for example,
of the already planned Qweak experiment at JLab
[12].
Acknowledgements
We acknowledge all the G0 collaboration and particularly
the students in charge of the analysis and
the analysis coordinator Fatiha Benmokhtar for
providing the material for this paper and the associated
talks.
References
[1] K.A Aniol et al., PRC70, 065501 (2004); K.A
Aniol et al., nucl-ex/0506010; Aniol et al., nuclex/0506011
[2] L.Bimbot “ The G0 parity violation experiment:
overview and status after the first commissioning
run“ proceedings NUPPAC03; L.Bimbot “First results
from the g0 parity violation experiment carried
out at JLab“ proceedings NUPPAC07.
[3] D.S.Armstrong et al., PRL95, 092001 (2005).
[4] D.Androic et al.,PRL104, 02001 (2010); arXiv:
0909.5107
[5] J.Liu, R.D.McKeown and M.J.Ramsey-Musolf,
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Lab. proposals E02-020, E05-008 and E08-
016.
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